In short. UCP and ACP cover overlapping commerce capabilities through distinct integration contracts that require platform-specific validation.
Definition: The Universal Commerce Protocol (UCP) and Agentic Commerce Protocol (ACP) define distinct integration contracts between AI agents and merchants. Their capabilities overlap, including checkout, but their request formats and platform requirements require separate implementation checks.
This comparison reflects official documentation reviewed on 17 October 2026.
Key facts
- The UCP specification defines cart, checkout, identity linking and order capabilities, with optional extensions layered onto capabilities.
- ACP's released specification index identifies a 2026-04-17 snapshot covering cart, feed, orders, authentication and Model Context Protocol (MCP), a protocol for exposing tools to clients.
- OpenAI's product feed reference treats checkout as a separately enabled integration and distinguishes supported Stable uploads from a Draft schema intended for planning and feedback.
Which capabilities overlap, and where do they differ?
UCP's Catalog capability defines product search and lookup operations. Platforms query a business catalog, then use returned variant identifiers in checkout. ACP's April release notes describe a feed push model: merchants send catalog metadata and product records to an agent-hosted service. The release also includes pre-checkout carts and order data covering fulfillment and adjustments.
A payment handler is a specification describing how payment instruments are processed. The UCP overview separates handlers from payment credential providers and negotiates capabilities through business and platform profiles. ACP's capability negotiation documentation places accepted payment handlers under capabilities.payment.handlers; the seller returns mutually supported interventions, such as payment authentication, and active extensions.
Both protocols therefore cover more than submitting an order. Catalog delivery direction, capability declarations and payment contracts remain concrete differences to assess when supporting both.
What changes in a merchant's checkout API?
An API is an interface through which software exchanges requests and responses. UCP's checkout REST binding specifies these creation and update operations:
POST /checkout-sessions
PUT /checkout-sessions/{id}
The ACP checkout schema for 2026-04-17 specifies:
POST /checkout_sessions
POST /checkout_sessions/{checkout_session_id}
The difference extends into payloads. UCP creation uses line_items containing an item object; ACP creation uses items containing item identifiers and quantities. UCP defines an update as full replacement of the checkout resource. These contracts imply separate request handling or translation even where an existing commerce backend supplies the prices and inventory.
Which published capabilities apply to Google and ChatGPT?
A transport binding maps protocol operations onto a communication mechanism. UCP's overview describes REST, MCP, Agent-to-Agent and embedded bindings. Google's native checkout guide specifies a REST API and supports multiple distinct line items in a session. Google's profile guide directs integrators to inspect its agent profiles for supported extensions and protocol versions.
ACP's published MCP binding maps checkout tools to its REST operations. OpenAI's Agentic Checkout Spec, however, documents REST endpoints for ChatGPT, describes MCP support as future work, and restricts Instant Checkout to approved partners. Protocol scope and a platform's accepted integration consequently need separate verification.
Related terms
- Agentic Commerce Protocol
- ChatGPT Instant Checkout
- Does submitting a catalog automatically enable Instant Checkout?
- Product feed freshness
FAQ
Can I reuse an existing UCP endpoint for ACP?
Compare its routes and payloads against ACP's checkout schema first. UCP uses hyphenated checkout paths and a PUT update; ACP uses underscored paths and a POST update.
Does an ACP product feed enable ChatGPT checkout?
OpenAI's product feed reference requires a separately enabled checkout integration. Its checkout documentation also requires partner approval for Instant Checkout.
How can I check Google's supported UCP extensions?
Inspect Google's agent profile for the target protocol version, as its profile guide recommends. Compare that declaration with the capabilities and extensions advertised by your business profile.
Sources
- UCP, "Universal Commerce Protocol (UCP) Official Specification", accessed 17 October 2026
- ACP, "Agentic Commerce Protocol (ACP)", accessed 17 October 2026
- OpenAI, "Products", accessed 17 October 2026
- UCP, "Catalog Capability", accessed 17 October 2026
- ACP, "Version 2026-04-17", 17 April 2026
- ACP, "Capability negotiation", accessed 17 October 2026
- UCP, "Checkout Capability - REST Binding", accessed 17 October 2026
- ACP, "Agentic Checkout API", version 2026-04-17
- Google, "Native checkout overview", accessed 17 October 2026
- Google, "Prepare your UCP profile", accessed 17 October 2026
- ACP, "MCP binding", version 2026-04-17
- OpenAI, "Agentic Checkout Spec", accessed 17 October 2026
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